Airlines can differentiate themselves, and consumers can select airlinesW, based on a number of ethical issuesW. For example, consumers might express their displeasure for a country by boycottingW its national airline. This article confines itself to the issue of climate change. Potential air travellers might respond to the issue of climate change by travelling less and/or by using other modes of transport which are more efficient (such as rail). This article further confines itself to the steps being taken by some airlines to offer services that are more "climate friendly" and the response of consumers to those services.

Air travel contributes significantly to climate change through a number of mechanisms,W in particular greenhouse gas emissions. Individual airlines and air travellers are currently utilizing/exploring two main approaches to reduce their impact on climate:

Carbon offsets: Paying others to achieve a counterbalancing effect on climate through activities outside the air transport sector. Note that the effectiveness of carbon offsetting is criticised.please expand

Reducing consumption of fossil fuels (air travel’s contribution to well-mixed greenhouse gasesW is completely dominated by the emission of carbon dioxide from burning fossil-derived aviation fuels[1],[2]). Two ways in which this can be done are:

Improve fuel efficiency.

Use a biofuel: This has a limited effect, and only if the biofuel has lower full-life-cycle greenhouse gas emissions. If additional greenhouse effects are caused by emitting aircrafts' exhaust gases at high altitudes, as is widely held[verification needed] then the relative benefits of biofuel are less.

Note: The only truly effective way to avoid the greenhouse impact of flying is to not fly.

Carbon offsetting organizations emerged into the mainstream in the latter half of the 1990s[3]. Today there are a large number of such organizations that passengers can use to offset a flight. Their products differ in method used to determine impact on climate, method used to offset impact on climate, price, and so on. Kollmuss and Bowell have compiled a review of the organizations and their products[4]. In recent years, the quantity of offsets sold has grown rapidly but the fraction of flights that are offset in this way remains negligible[5] (and this is despite the fact that the cost of an offset is typically of order only 1% of the cost of an airfare[6]).

Airlines can offer carbon offsets to their passengers (in such a program, passengers that wish to participate pay the airline an additional charge — the airline then uses the money to purchase appropriate offsets for the passenger’s flight from a carbon offsetting organization). British AirwaysW was the first major airline to establish such a program (in September 2005)[7],[8]. Initially British Airways kept its program largely hidden from its passengers, resulting in very low passenger participation. This was later criticised by the British government[9]. Since then many more airlines have introduced offset programs. For example, in June 2007 Delta Air LinesW became the first major U.S. airline to introduce such a program[10]. Airlines have also become much more aggressive at marketing their programs to passengers. For example, since September 2007, passengers booking flights over the internet or telephone with Jetstar AirwaysW have been required to specify whether or not they wish to purchase offsets for their flight[11] (an example of "mandated choice"[12]). With this approach, Jetstar has secured approximately 10% passenger participation[13],[14] (Jetstar’s offsets typically add approximately 1% to the price of the airfare[15]). British Airways also adopted this approach (in January 2008)[8]. Virgin AtlanticW has (since November 2007) promoted its offset program while in flight[16]. Virgin AmericaW has (since January 2009) done the same thing using its inflight entertainment system[17].

Note that an approach such as Jetstar's makes participation far easier for the customer, with an easy opt-in, actively informing customers (who are no doubt surprised by how little the offsets cost) and reassuring them that there is an actual environmental value in the offset (~"Australian Greenhouse Office approved").

A small number of airlines, operating in niche markets, offset all of their flights. The airfares of such airlines include a mandatory component to cover the cost of offsetting. Examples of such airlines are Nature AirW (since 2004[18]), Harbour AirW (since 2007[19]), and (now defunct) SilverjetW (in 2007W). Such airlines strongly promote their ‘carbon neutral’ status.

Several airlines have made demonstration flights using biofuels — Virgin AtlanticW in February 2008[21], Air New ZealandW in December 2008[22], and ContinentalW and Japan Airlines in January 2009[23],[24].

In November 2009, KLM became the first airline to perform a passenger-carrying flight using biofuel[25].

If even one airline can operate on a biofuel blend on one of its routes, then it becomes possible for any airline to offer any passenger flying on any route the option to effectively fly on a fuel that emits no greenhouse gas[26]. Equivalently, the airline industry could create carbon offsets (and could therefore offer carbon offsets to passengers without needing to employ carbon offsetting organizations that are not part of the airline industry).

The use of biofuels might address greenhouse gas emissions, but it also raises other issuesW (such as competition over land/ocean with ecosystem conservation, use of agricultural chemicals, treatment of agricultural workers, and so on). Even if these issues can be addressed, there remains a conflict between devoting resources to air travel and devoting resources to purposes that might be regarded as more essential (for example, a person can be trained to fly wealthy tourists or trained to develop agricultural systems in impoverished communities). Defining what might constitute ‘green’ air travel therefore remains challenging (especially in the case of leisure travel).